The ultimate goal of the prospective studies is to understand the nature of the mechanisms underlying the aging process in animals. The objective of the proposed studies is to test the predictions of the free radical hypothesis of aging. The relationship between rates of oxy-radical generation and aging will be explored by pursuing three different lives of investigation: (1) Determine if rates of O2 and H2O2 generation by mitochondria increase during aging in mammalian and insect species. (2) Determine if rates of O2 and H2O2 generation by mitochondria are correlated with variations in life span of different mammalian and insect species. Comparisons will be made within rather than between the phylogenetic groups. (3) Investigate why the rates of O2 and H2O2 generation by mitochondria vary in different tissues and species. Results of this study will promote a better understanding of the relationship between oxy-radical and hydroperoxide production by mitochondria and the aging process.